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Rocks a naturally occurring solid aggregate of one or more minerals or mineraloids Granite is a combination of biotite, feldspar and quartz minerals. The ROCK CYCLE represents the processes of continuous changes that connect the three major groups of rocks SEDIMENTARY IGNEOUS METAMORPHIC two important parts of the “Rock Cycle” are SEDIMENTS and molten LAVA and MAGMA Another version of the Rock Cycle IGNEOUS ROCKS • Form by solidification (crystallization) of melted minerals • At the surface, LAVA hardens to form EXTRUSIVE rocks with tiny (FINE-GRAINED) crystals or GLASSY (no crystal) TEXTURES • Beneath the surface, MAGMA hardens to form INTRUSIVE rocks with easily visible (COARSEGRAINED) crystal texture. Granite Intrusive Igneous Rock • Light-colored, coarsegrained, no pattern • Mostly quartz, feldspar, mica, and hornblende • Often used for buildings and monuments Basalt Extrusive Igneous Rock • Dark-colored, finegrained • Formed where lava erupted onto surface • Most widespread igneous rock • Vesicular Basalt forms when dissolved gases are forced out of solution Obsidian Extrusive Igneous Rock • Natural volcanic glass • Forms when lava cools very quickly • Fractures along curved (conchoidal) surface • High in silicates Pumice Extrusive Igneous Rock • Pumice is created when super-heated, highly pressurized rock is violently ejected from a volcano. • Consists of highly vesicular rough textured volcanic glass, which may or may not contain crystals. • Typically light colored Sedimentary Rocks Formed by the deposition of material at the Earth's surface and within bodies of water. • Clastic sedimentary rocks, • Biochemical (or biogenic) sedimentary rocks • Chemical sedimentary rocks • “Other" sedimentary rocks formed by impacts, volcanism, and other minor processes Clastic Rocks Made of cemented sediment, classified by their grain sizes. • Conglomerate • Sandstone Shale • Formed from compaction. • Composed of mud • Shales are typically deposited in very slow moving water - often found in lakes and lagoonal deposits, in river deltas, on floodplains and offshore from beach sands. • Breaks into thin sheets Chemical Sedimentary Rocks formed from precipitation (settling out from a solution) Limestone is made from calcite Biochemical Sedimentary Rocks come from the remains of organic matter. • The most important of these is coal. • Formed from dead vegetation under high pressure and temperature. Metamorphic Rocks • Formed by heat and pressure changing existing rocks • REGIONAL METAMORPHIC affects a large area and results from plate tectonics • CONTACT METAMORPHISM affects rocks on a local scale, such as “baking” sedimentary rocks next to magma or lava Foliated Metamorphic Rocks contain minerals that produce layering or banding Schist: medium-grained rock contains mica Slate: fine-grained, foliated, homogeneous rock derived from an original shale-type sedimentary rock composed of clay or volcanic ash Non-foliated metamorphic rocks Rocks that were subjected to uniform pressure from all sides, or those that lack minerals with distinctive growth habits, will not be foliated Quartzite • Formed from sandstone • Pure quartzite is usually white to gray • Pink and red quartzites occur due to varying amounts of iron oxide (Fe2O3).
